Deep in Texas, a plant-eating feathered dinosaur reemerges

By Eric Gershon

April 29, 2013

A recently identified feathered dinosaur found deep in West Texas reinforces an emerging view that creatures like it were more diverse and widespread in North America than previously thought, according to a new study.

The species — a turkey-sized herbivore called Leptorhynchos gaddisi — belongs to a broader group of bird-like dinosaurs characterized by toothless beaks and long, slender claws, said researchers, who analyzed fossils found near Big Bend National Park at a site dating to about 75 million years ago.

The broader group to which Leptorhynchos (“little jaw”) belongs — the bird-like caenagnathids — was previously known from fossils found in Asia, western Canada, and Utah. The Texas fossils represent the southernmost evidence of caenagnathids in North America, expanding their known range and variety.

“We have a pretty good understanding of what the larger dinosaurs looked like,” said Nicholas R. Longrich, a postdoctoral researcher at Yale University and lead author of the paper, published April 26 in the Bulletin of the Peabody Museum of Natural History. “We have a much poorer picture of small dinosaurs. Leptorhynchos helps fill in the gap. It also supports the idea that there were different dinosaur species in different regions. We’re just starting to scratch the surface in terms of dinosaur diversity. It’s not all giant horned beasts.”

In the paper, Longrich and co-authors also reassess the evolutionary history of North American caenagnathids and offer a revised classification system that expands the total number of species to at least six, from three or four previously recognized. They used jaw bones as the primary point of differentiation. Leptorhynchos adds to the new total, as does the resurrection of an older species, Caenagnathus collinsi.

“The remarkable thing about caenagnathids is that they had a wide range of beak shapes — like modern birds, and specifically Darwin’s finches,” said Longrich. “Each species has a different beak structure. You could have a lot of different species in one environment because they ate different kinds of foods, which is how different species of Darwin’s finches coexist. So, in a way, the evolution of modern dinosaurs — birds — provides insight into ancient, extinct dinosaurs.”

Leptorhynchos was identified and distinguished from closely related species primarily on the basis of its jaw proportions and shape. The chin is more rounded than the chin of its Canadian relative, Leptorhynchos elegans, and the beak is not as strongly upturned.

“These are subtle differences, but they mean we’re dealing with different species,” said Longrich. “If you look at modern birds, one of the things that distinguishes a crow from a raven, or two types of albatrosses from each other, is the beak proportions. We can do the same thing with dinosaurs that we do with modern birds, and identify them using beak shapes.”

Fossil collectors Ken Barnes, Scott Clark, and Larry Millar of Texas discovered the new fossils in the Aguja Formation, near Terlingua, Texas, just outside of Big Bend National Park. The Aguja Formation has previously yielded the horned dinosaur Agujaceratops and the small bone-headed dinosaur Texacephale. The site is generally considered to be about 71-84 million years old. The collectors, all based in Texas, have been searching the site for 14 years, often with student volunteers from local high schools.

The paper is titled “Caenagnathidae from the Upper Campanian Aguja Formation of West Texas, and a Revision of the Caenagnathinae.” The Yale Institute for Biospheric Studies supported the research.